The present invention relates to a self test system for use with an ultrasonic transducer mounted on a wave guide plate assembly or wall and which is used for contaminant detection. The ultrasonic transducer is bonded to the wave guide wall or plate, or other wave guide, and the self test procedure determines that the transducer is working and whether the transducer is aconstically bonded or coupled to the wall or pale.
In the prior art, acoustic channels or wave guides that have ultrasonic transducers bonded to one location, that transmit signals that are reflected from a reflector positioned at a spaced location have been known. The wave guide generally comprises a plate or sheet that has a surface exposed to ambient conditions. Snow, ice, or other contaminants that adhere to the exposed surface will cause changes (attenuation) in the reflected wave that is sensed by the transducer. The changes in the reflected wave indicate the presence of ice, as well as other contaminants.
U.S. Pat. No. 5,922,958 to Schugt shows such a detector device. The weakening or loosening of the bond between the transducer or transmitter and the plate can occur and some way of checking for adequate ultrasonic vibration coupling to the plate is. desired. When a sensor disbonds or in some way the bond fails the ultrasonic sensors will give spurious or no signals and a shortened sensor life. If there is heavy plate contamination, the guided wave signature or reflected signal received from the reflector near the end of the plate disappears, which can indicate that either the plate is truly contaminated, the transducer is not working, or a disbond occurred. The present invention provides a simple self test procedure that will provide information about the integrity and performance of ruse bond of the transducer, as well as its ability to function for determining contaminants on a surface of a wall or plate. Contaminant detected systems are also shown in Rose et al. U.S. Pat. Nos. 5,629,485 and 5,932,806.
The present invention relates to an ultrasonic vibration sensor, preferably formed as a wall or plate with a surface exposed to ambient elements, and which has an ultrasonic transducer, including a transmitter bonded to the wall or plate. The transmitter and a receiver for reflected or returned ultrasonic vibration can be combined and placed at one location, generally adjacent one end of a plate. An ultrasonic or acoustic vibration reflector is placed at a location spaced from the transmitter. Preferably, the reflector has a surface extending transversely to the direction of transmission of the ultrasonic energy at the opposite end of the sensor wall. The reflector, as shown may be a block bonded to the wall or plate.
A self test procedure is provided by placing a second known discontinuity, as shown a waveguide, in the plate or wall adjacent the ultrasonic vibration transmitter. The second discontinuity forms an ultrasonic wave reflector that will reflect any wave transmitted from the transducer. The preferred construction is a small waveguide bonded to the under surface of the wall or plate. Wave displacements normal to the plate surface would transfer into the waveguide, hit the end of the waveguide and reflect back toward the transducer. Other known reflectors close to the transmitter or transducer can be used. The second ultrasonic wave reflector that is positioned close to the transmitter is of less a disruption than the contaminate signal generating reflector near the end of the sensor wall. Because the test reflector is close to the transmitter, the signal received from the self test reflector is not attenuated by ice or other contaminants adhering to the opposite side of the wall or plate. The receiver circuit provides a signal indicating receipt of the signal reflected from the second discontinuity.
A processor circuit is connected to receive the signal related to the reflected wave from the second discontinuity. The process converts the signal that is received from the self test reflector into a readout indicating the transmitter is operating. If the transmitter has a failure or it has disbonded, there will be no signal.
Again, the self test reflector is close enough to the transmitter portion of the transducer so even with contaminants adhering to the exposed surface of the transmission wall or plate there will be a signal shape that will not change unless there is a disbond or other problem with the ultrasonic transducer itself. The length of the self test waveguide forming a reflector that is in contact with and bonded to the plate or wall is related to the wavelength of the ultrasonic energy in the plate to insure that the ultrasonic energy is transferred to the waveguide. Also, the overall length of the self test waveguide forming the self test reflector is selected to provide a time before having a return signal from the self test reflector so that any disturbances from internal reflection in the transducer or transducer mounting are abated. This insures that the internal reflections are not confused with or thought to be signals from the self test waveguide.
The self test reflector arrangement is easily formed or installed, and serves as a integrity check each time the transducer transmits an ultrasonic signal toward the contaminant detector.
It should be noted that while the preferred embodiment illustrates a bonded on waveguide for the self test and a bonded on block for the main contaminant detection, other types of reflectors can be utilized. For example, the surface on the plate opposite from the surface exposed to ambient conditions can have a groove or other known type formed in the plate. A rivet array in the wall can serve as the self test reflector as well. Further, the wall of a structure can transmit the ultrasonic signal, so a separate plate is not always necessary. The first reflector used for detecting contaminates can be replaced by a separate receiver positioned on wall or plate at the location disclosed for the reflector.